Perforating gun with switch cartridge

ABSTRACT

An apparatus for selectively firing a perforating gun having a plurality of gun assemblies includes a plurality of cartridge assemblies. Each cartridge assembly is associated with a gun assembly of the plurality of gun assemblies. Each cartridge assembly includes a body having a cavity, an input contact configured to receive a signal, and a throughput contact configured to convey the signal. The perforating gun may include a carrier and at least one bulkhead.

TECHNICAL FIELD

The present disclosure relates to devices and method for perforating a subterranean formation.

BACKGROUND

Hydrocarbons, such as oil and gas, are produced from cased wellbores intersecting one or more hydrocarbon reservoirs in a formation. These hydrocarbons flow into the wellbore through perforations in the cased wellbore. Perforations are usually made using a perforating gun that is generally comprised of a steel tube “carrier,” a charge tube riding on the inside of the carrier, and with shaped charges positioned in the charge tube. The gun is lowered into the wellbore on electric wireline, slickline, tubing, coiled tubing, or other conveyance device until it is adjacent to the hydrocarbon producing formation. Thereafter, a surface signal actuates a firing head associated with the perforating gun, which then detonates the shaped charges. Projectiles or jets formed by the explosion of the shaped charges penetrate the casing to thereby allow formation fluids to flow through the perforations and into a production string.

In certain instances, it may be desirable to use switches to selectively fire guns in a perforating tool. The present disclosure addresses the need to house or otherwise accommodate such switches in a downhole tool.

SUMMARY

In aspects, the present disclosure provides an apparatus for use in a wellbore. The apparatus may include a first gun assembly and a second gun assembly.

The first gun assembly may have: a first charge tube having a longitudinal axis defined by an axis that passes through centers of opposing ends of the charge tube; a first detonator cord disposed along the first charge tube, a first signal-conveying wire disposed along the first charge tube, a first coupler affixed to an end of the first charge tube, the first coupler including: a receptacle receiving an end of the detonator cord, and a coupler contact electrically connected to the first signal conveying wire, and a first cartridge assembly including: a body having a cavity and a cradle, an input contact positioned on the body and electrically coupled to the coupler contact, a throughput contact positioned on the body, a switch disposed in the cavity, the switch being electrically connected to the input contact and the throughput contact, and an initiating element disposed in the cradle and electrically connected to the switch, the initiating element being energetically coupled to the end of the detonator cord in the receptacle, wherein the switch and the initiating element at least partially overlap along the longitudinal axis; and a first signal transfer assembly electrically coupled to the throughput contact.

The second gun assembly may have: a second charge tube, a second detonator cord disposed along the second charge tube, a second signal-conveying wire disposed along the second charge tube, the second signal-conveying wire being electrically coupled to the first contact assembly, a second coupler affixed to an end of the second charge tube, the second coupler including: a receptacle receiving an end of the second detonator cord, and a coupler contact electrically connected to the second signal conveying wire; and a second cartridge assembly including: a body having a cavity, an input contact electrically positioned on the body and coupled to the second coupler contact, a throughput contact positioned on the body, a switch disposed in the cavity, the switch being electrically connected to at least the input contact, and an initiating element disposed in the cavity and electrically connected to the switch, the initiating element being energetically coupled to the end of the second detonator cord in the receptacle.

In aspects, the present disclosure also provides an apparatus for use with a gun assembly having charge tube with a longitudinal axis defined by an axis that passes through centers of opposing ends of the charge tube, a detonator cord disposed along the first charge tube, and a signal-conveying wire disposed along the first charge tube. The apparatus may include: a switch having an initiating element; a coupler configured to be received at an end of the first charge tube, the first coupler including: a receptacle receiving an end of the detonator cord, and a coupler contact electrically connected to the first signal conveying wire; and a cartridge assembly engagable with the first coupler, the cartridge assembly including: a body having a cavity configured to receive the switch and a cradle configured to receive the initiating element, an input contact positioned on the body, and a throughput contact positioned on the body, wherein engaging the cartridge assembly with the coupler simultaneously electrically couples the input contact to the coupler contact and energetically couples the initiating element with the end of the detonator cord, and wherein the switch and the initiating element are positioned in a parallel, side-by-side arrangement to at least partially overlap along the longitudinal axis.

In aspects, the present disclosure provides a perforating gun. The perforating gun may include a carrier and at least one bulkhead. The carrier may have at least two sections connecting to one another at a connection. There are no sealing members between the two sections at the connection. The bulkhead is disposed within the carrier and has at least one sealing member forming a seal between the bulkhead and an inner surface of the carrier.

It should be understood that certain features of the invention have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will in some cases form the subject of the claims appended thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

For detailed understanding of the present disclosure, references should be made to the following detailed description taken in conjunction with the accompanying drawings, in which like elements have been given like numerals and wherein:

FIG. 1 schematically illustrates a side sectional view of a perforating gun with a switch cartridge according to one embodiment of the present disclosure;

FIG. 2 isometrically illustrates the FIG. 1 embodiment without a carrier;

FIG. 3 schematically illustrates a side sectional view of portion of the FIG. 1 embodiment;

FIGS. 4A-B illustrate a coupler according to one embodiment of the present disclosure;

FIGS. 5A-B illustrate one embodiment of a cartridge assembly according to the present disclosure;

FIGS. 6A-B schematically illustrate prior art switches;

FIG. 7 illustrates a side sectional view of an interface between a bulkhead and a cartridge assembly according to one embodiment of the present disclosure;

FIG. 8 illustrates a side sectional view of an interface between a coupler and a cartridge assembly in accordance with one embodiment of the present disclosure;

FIG. 9 schematically illustrates a side sectional view of a perforating gun with a switch cartridge according to another embodiment of the present disclosure;

FIG. 10 isometrically illustrates the FIG. 9 embodiment without a carrier;

FIG. 11A-C illustrate another coupler according to the present disclosure;

FIGS. 12A-B illustrate another embodiment of a cartridge assembly according to the present disclosure;

FIG. 13 illustrates a side sectional view of an interface between a bulkhead and the FIGS. 12A-B cartridge assembly according to one embodiment of the present disclosure; and

FIG. 14 illustrates a side view of another arrangement of the FIG. 9 perforating tool according to one embodiment of the present disclosure.

DETAILED DESCRIPTION

The present disclosure relates to devices and methods for perforating a formation intersected by a wellbore. The present disclosure is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present disclosure with the understanding that the present disclosure is to be considered an exemplification of the principles of the disclosure, and is not intended to limit the disclosure to that illustrated and described herein.

Referring to FIG. 1, there is shown one embodiment of a perforating tool 100 in accordance with the present disclosure. The perforating tool 100 may include a first gun assembly 110 and a second gun assembly 112. Each gun assembly 110, 112 includes a carrier 111 that is shaped to receive a charge tube 114. Each gun assembly 110, 112 also includes one or more shaped charges 116 fixed within the charge tube 114. To enable selectively firing the gun assemblies, a select fire system may be used in which a cartridge assembly 200 a is programmed to only fire the first gun assembly 110 and a cartridge assembly 200 b is programmed to only fire the second gun assembly 112. While two gun assemblies 110, 112 are shown, three or more gun assemblies and associated cartridge assemblies may be used.

Generally, the perforating tool 100 is lowered into a wellbore (not shown) on electric wireline, slickline, tubing, coiled tubing, or other conveyance device (not shown) until it is adjacent to the hydrocarbon producing formation (not shown). Thereafter, a surface signals are used to actuate the gun assemblies 110, 112, which then detonate the associated shaped charges. Projectiles or jets formed by the explosion of the shaped charges penetrate a casing (now shown) lining a wellbore (not shown) to thereby allow formation fluids to flow through the perforations and into a production string (not shown). Illustrative arrangements according to the present disclosure for enabling select firing of the gun assemblies 110, 112 are described below.

Referring now to FIG. 2, a gun assembly 110 in accordance with one embodiment of the present disclosure is shown in an isometric view. For clarity, the carrier 111 (FIG. 1) is not shown. In this embodiment, the charge tube 114 may be formed as a tubular member having a first end 118, a second end 120, and an interior bore 122. The charge tube 114 provides a receiving structure in which the shaped charges 116, a bulkhead 130 a, a coupler 160 a, and the cartridge assembly 200 a (FIG. 1) are secured. The bulkhead 130 a may be fixed to the first end 118 with a suitable fastening element 132, such as a screw.

The charge tube 114 may include a first opening 148 through which the shaped charge 116 may be inserted into the interior bore 122 and a second opening 150 through which the coupler 160 a may be inserted into the interior bore 122. Depending on the configuration of the coupler 160 a, a third opening 152 (FIG. 3) may be present through which a portion of the coupler 160 a may project out of the charge tube 114.

Referring to FIGS. 1 and 3, the bulkhead 130 a acts a structural barrier between sections of the perforating tool 100. In embodiments, the bulkhead 130 a may be a disk-like member having an outer circumferential surface 134 (FIG. 3) and a passage 136 (FIG. 3). The bulkhead 130 a may include an alignment key 143 fixed on the outer surface 134 that is complementary to a keyway 145 (FIG. 1) formed along an inner surface 147 of the carrier 111. The keyway 145 may be a slot, groove, or other similar surface depression that has a specified angular orientation relative to one or more features of the perforating gun 110, e.g., a scallop 149 or another reduced thin wall section of the carrier 111. Thus, upon the alignment key 143 entering the keyway 145, the shaped charge 116, which has a fixed angular alignment relative to the alignment key 143, can be aligned with the scallop 149.

As shown in FIG. 1, the charge tube 114 is sealed between the opposing bulkheads 130 a,b inside the carrier 111. In one arrangement, one or more seals 138 may be disposed on the outer circumferential surface 134. The seals 138 provide an interior of the carrier 111 that is fluid-tight. The passage 136 of the bulkhead 130 a is shaped to receive an signal transfer assembly 146 a. The signal transfer assembly 146 a is configured to transmit signals across the bulkhead 130 a or other structural barriers in the perforating tool 100 (FIG. 1). The signal transfer assembly 146 a also has seals 139 to form a fluid-tight seal in the passage 136. An signal transfer assembly 146 b is configured to transmit signals across the bulkhead 130 b and is generally similar to the signal transfer assembly 146 a. The bulkhead 130 b may have the same construction as the bulkhead 130 a.

Referring to FIGS. 3 and 4 A,B, there is shown a coupler 160 a in accordance with one embodiment of the present disclosure. The coupler 160 a provides two operative connections when engaged with the cartridge assembly 200 a (FIG. 1). The first connection is an energetic connection between a detonator cord 174 and the cartridge assembly 200 a (FIG. 1). As used herein, an “energetic connection” or “energetic coupling” is a connection or coupling that enables the transmission of sufficient energy, such as thermal energy, to detonate the detonator cord 174. The second connection transfers power (e.g., electrical power) and/or signals (e.g., control signals), hereafter collectively “signals,” from the signal transfer assembly 146 a to the cartridge assembly 200 a (FIG. 1). The coupler 160 b provides similar operative connections for the cartridge assembly 200 b (FIG. 1).

Referring to FIGS. 4A,B, in one embodiment, the coupler 160 a may include a body 162 on which a coupler contact 167 is positioned. The coupler contact 167 may include a coupler contact surface 164 and a wiring contact 166. As illustrated, the coupler contact surface 164 is formed on a coil spring disposed on a tubular receptacle 168 of the body 162. However, other coupler contact surfaces 164 configured for compressive engagement, such as on leaf springs, may be used. In still other embodiments, the coupler contact surface 164 may not use a biasing feature; i.e., a feature that provides a biasing force. The wiring contact 166 may be any type of fastener, hook, frame, or other member that can be affixed to the body 162 and has at least a portion that is electrically conductive. A coupler 160 b is generally of the same construction as that of the coupler 160 a.

Referring to FIGS. 5A-B, there is schematically shown a cartridge assembly 200 a in accordance with one embodiment of the present disclosure. Cartridge assembly 200 b may use a similar configuration as cartridge assembly 200 a. As will be apparent from the discussion below, the cartridge assembly 200 a acts as a structural and electrical adaptor that enables switches of various different configurations and sizes to be used in the perforating tool 100. Exemplary switches 180, 181 that may be operatively connected to the cartridge assembly 200 a are shown in FIGS. 6A-B.

Referring to FIG. 6A, the switch 180 may be any conventionally constructed electrical device that, in response to a received signal, can output sufficient thermal energy to detonate an energetic material such as that used in the detonator cord 174 (FIG. 3) or the booster 172 (FIG. 3) and/or transmit, re-transmit, or otherwise convey an electrical signal. One class of switches are considered “select fire” switches because they can be programmed to initiate the firing of one perforating gun of a plurality of perforating guns or the firing of a sub-set of perforating guns of sets of perforating guns. The switch 180 may include analog and/or digital circuitry configured to receive and interpret signals. Interpreting signals may be as simple as recognizing polarity or comparing a received signal with a preprogrammed code or pattern. Irrespective of the configuration, the switch 180 either initiates the firing of the associated perforating gun or passes the signal to the next switch 180 based on the received signal.

A conventional construction may include a body 182 that has an electrical input 184, an electrical output 186, and an initiating element 188. The electrical input 184 may be a wire, terminal, pad, or other structure to which a wire, node, pad, or such structure can be electrically connected. The electrical output 186 may also be a similarly configured wire, terminal, a node, or a pad. The initiating element 188 applies activating energy for detonating the detonator cord 174 or booster 172 in response to an activation signal (e.g., electrical energy). In some embodiments, the initiating element 188 may be metal rod or similar member that generates heat with the application of electrical energy. Wires 190, 192 connect the initiating element 188 to the body 182 of the switch 180. Thus, the initiating element 188 may be positioned at a location that is different from where the body 182 is positioned. The switch 180 may also include a ground wire 194.

Referring to FIG. 6B, another prior art switch 181 may include a body 183 that has an electrical input 185, an electrical output 187, and an initiating element 189. The electrical input 185 may be a wire, terminal, pad, or other structure to which a wire, node, pad, or such structure can be connected. The electrical output 187 may also be a wire, terminal, a node, or a pad. The initiating element 189 applies activating energy for detonating the detonator cord 174 or booster 172 in response to an activation signal (e.g., electrical energy). In some embodiments, the initiating element 189 may be metal rod or similar member that generates heat with the application of electrical energy. In this embodiment, the initiating element 189 is integral with the body 183 and, therefore, co-located with the body 183. The switch 181 may also include a ground wire 195.

It is emphasized that the present disclosure is not limited to any particular switch design or initiating element. To the contrary, with the benefit of the present teachings, one skilled in the art will appreciate that the devices of the present disclosure can be readily adapted to accommodate a wide variety of switches that employ different electrical and physical configurations. Also, for brevity, reference to the switch 180 is inclusive of a reference to the switch 181 (FIG. 6B).

Referring to FIG. 5A-B, the cartridge assembly 200 a includes a body 202 in which a cavity 204 is formed and an electrical assembly 206 for communicating signals to and from the switch 180 (FIG. 6A). The cavity 204 is sized and shaped to house the switch 180 (FIG. 6A). In one arrangement, the electrical assembly 206 forms electrical connections with the switch 180 (FIG. 6A) using a throughput contact 208 and an input contact 210.

The input contact 210 conveys a received signal to the switch 180 (FIG. 6A) inside the cartridge assembly 200 a. The input contact 210 may include an external input contact 222 and a wire 224. The external input contact 222 may be a screw or other fastening element that is fixed to a second face 226 of the body 202 and is electrically connected to the wire 224. The external input contact 222 may be sized to present a suitable contact surface 230 for physically contacting the coupler contact surface 164 (FIG. 3). The wire 224 has an end 228 that leads to the cavity 204. The end 228 may be electrically connected to the electrical input 184 (FIG. 6A) of the switch 180 (FIG. 6).

The throughput contact 208 conveys the signal received by the cartridge assembly 200 a to another cartridge assembly, here cartridge 200 b. The signal may be the same as or similar to the received signal or a new signal. The throughput contact 208 may include a external throughput contact 212, an eyelet 214, and a wire 216. The external throughput contact 212, may be a disk or plate that is fixed using the eyelet 214, or other suitable device, to a first face 218 of the body 202. The eyelet 214 may be a screw or other fastening element that is also fixed to the first face 218 and is electrically connected to the external throughput contact 212 and the wire 216. The wire 216 has an end 220 that terminates within or near the cavity 204. The end 220 may be electrically connected to the electrical output 186 (FIG. 6A) of the switch 180 (FIG. 6). In certain embodiments, the external throughput contact 212 may be formed as a compressive element that acts as a biasing member; e.g., a spring. In such embodiments, the external throughput contact 212 applies a compressive force to the cartridge 200. Thus, the compressive force applied by the external throughput contact 212 and/or the coupler contact surface 164 (FIG. 3) may be used to ensure that the cartridge assembly 200 compressively engages the coupler 160. This compressive engagement ensures that signals and activation energy (e.g., thermal energy) can be transferred between the cartridge assembly 200 and the coupler 160

In embodiments, the cartridge assembly 200 may also include an electrical grounding assembly 240 for grounding the switch 180 (FIG. 6). The grounding assembly 240 may include a contact element 242 positioned in the cavity 204, an external ground contact 244, and a wire 245 electrically connecting the contact element 242 to the external ground contact 244. The external ground contact 244 may be electrically connected to a biasing member 246 that is in contact with an inner surface of the charge tube 114 (FIG. 2). In one arrangement, the cartridge assembly 200 may use a metal bow spring as the biasing member 246.

Referring to FIGS. 2 and 5A-B, in embodiments, the cartridge assembly 200 a may be secured in the charge tube 114 with a mechanical interlocking mechanism. For example, the second end 120 of the charge tube 114 may include a “J” slot 250 that is shaped and dimensioned to be complementary to a post 252 that projects out of the body 202.

It should be appreciated that the switch 180 (FIG. 6A) may be pre-installed in the cartridge assembly 200 a prior to assembly of the perforating tool 100. This pre-installation may include making electrical connections between the electrical input 184 and electrical output 186 (FIG. 6A) of the switch 180 (FIG. 6A) and the wires 224, 220 (FIG. 5B), respectively, of the cartridge assembly 200 a (FIG. 5B). Conventionally, making such electrical connections may require twisting of wires, soldering, etc. Advantageously, in embodiments of the present disclosure, such activity is done beforehand between the switch 180 (FIG. 6A) and the cartridge assembly 200 a. Later installation simply requires sliding or otherwise positioning the cartridge assembly 200 a inside the perforating tool 100 to engage the coupler 160 and form the electrical connections. Here, the engagement occurs by positioning the cartridge assembly 200 a into a side-by-side relative relationship. These electrical connections may be formed by electrically conductive surfaces that are in physical contact, and possibly in compressive contact, or sufficiently close as to allow the transmission of electrical signals. Moreover, the energetic connection that enables the transfer of thermal energy may also be formed by the same installation action.

The gun assembly 112 also includes similar features, e.g., a cartridge assembly 200 b, a bulkhead 130 b, a coupler 160 b, etc. and uses the same construction as gun assembly 110, although in other embodiments a different construction may be used.

An exemplary use of the perforating tool 110 be described with reference to FIGS. 1-8.

Referring to FIG. 1, the perforating gun 100 has an uphole end 280 and a downhole end 282. The uphole end 280 connects to a conveyance device such as a wireline (not shown), which extends to a surface location. The downhole end 282 points a well bottom (not shown). While two gun assemblies 110, 112 are shown between the ends 280, 282, three or more gun assemblies, each with one or more shaped charges 116, may be present. In one exemplary mode of operation, the perforating gun closest to the downhole end 282, here perforating gun 112, is fired first. Thereafter, the next most adjacent perforating gun uphole of the fired perforating gun, here perforating gun 110, is fired. To facilitate sequential “bottom up” firing of the perforating tool 100, multiple firing signals may be sent. For instance, a first firing signal may be sent to fire the perforating gun 112 and a second firing signal may be sent to fire the perforating gun 110. As further described below, the cartridge assembly 200 a is programmed to pass the first firing signal to the cartridge 200 b. The cartridge 200 b is programmed to fire the perforating gun 112 upon receiving the first firing signal. The cartridge 200 a is programmed to fire the perforating gun 110 upon receiving the second firing signal. If more than two gun assemblies are present, then three or more cartridge assemblies and associated firing signals may be needed.

Referring to FIG. 1, to initiate firing, the first firing signal may be transmitted from a surface location to the perforating gun 100 by a signal conducting carrier 290. A signal receiving interface for receiving the first firing signal is provided in an end cap 292. The end cap 292 may be a disk-like closure member attached to the uphole end 280 of the perforating tool 100. The signal transfer assembly 146 a includes a signal conducting tip 251 on one end and a connection with a wire 176 a at the other end. The wire 176 a is in signal communication with the cartridge assembly 200 a via the coupler 160 a. Therefore, when the tip 251 electrically engages the signal conducting carrier 290, a signal conducting circuit is formed across the bulkhead 130 a such that the first firing signal can be communicated from the signal conducting carrier 290 to the coupler 160 a.

The signal transfer from the signal transfer assembly 146 a to the coupler 160 a is illustrated in FIG. 8. In one arrangement, a signal conducting circuit is formed by the wire 176 a and a coupler contact 167. The wire 176 a and the coupler contact 167, which includes the wiring contact 166 and the coupler contact surface 164, are all formed of an electrically conductive material, such as a metal, and are electrically connected to one another using suitable known electrical connections. In this arrangement, the body 162 is made of an electrically non-conductive material, e.g., a non-metal such as a plastic. The first firing signal travels via the wire 176 a to the wiring contact 166 and then to the coupler contact surface 164. The electrical connection between the coupler contact surface 164 and the external input contact 222 of the input contact 210 transfers the first firing signal to the input contact 210 of the cartridge 200 a.

Referring to FIGS. 5A,B, the first firing signal travels from the external input contact 222 via the wire 224 to the electrical input 184 (FIG. 6A) of the switch 180 (FIG. 6A). Because the switch 180 (FIG. 6A) is programmed to fire the gun assembly 110 (FIG. 1) only after receiving the second firing signal, the switch 180 (FIG. 6A) passes the first firing signal to the throughput contact 208 via the electrical connection to the wire 216. The first firing signal travels via the wire 216 to the eyelet 214 and the external throughput contact 212.

FIG. 7 illustrates the signal transmission interface and signal transfer from the external throughput contact 212 of the cartridge assembly 200 a to contact assembly 146 b in the bulkhead 130 b. The contact assembly 146 b includes a signal conducting tip 251 on one end and a connection with a wire 176 b at the other end. The wire 176 b is in signal communication with the cartridge assembly 200 b via a coupler 160 b (FIG. 1). Therefore, when the tip 251 contacts the external throughput contact 212 of the cartridge assembly 200 a, a signal conducting circuit is formed across the bulkhead 130 b such that the first firing signal can be communicated from the cartridge assembly 200 a of the perforating gun 110, via the coupler 160 b, to the cartridge assembly 200 b of the perforating gun 112 (FIG. 1).

The electrical connection between the contact assembly 146 b in the bulkhead 130 b and the coupler 160 b and the electrical connection between the coupler 160 b and the cartridge assembly 200 b is similar to that already described in connection with FIGS. 8 and 7, respectively. The first firing signal travels through these electrical connections to the input contact 210 of the cartridge assembly 200 b.

Referring to FIGS. 5A,B, the first firing signal is received at the external input contact 222 and transmitted by the wire 224 to the electrical input 184 (FIG. 6A) of the switch 180 (FIG. 6A). Because switch 180 (FIG. 6A) is programmed to recognize that the first firing signal is for firing the perforating gun 112, the switch 180 initiates the firing of the perforating gun 112.

Referring to FIG. 3, the firing of the perforating gun 112 is performed by using a detonation-transfer type energetic connection between the cartridge assembly 200 b (FIG. 1) and the coupler 160 b, which is the same as coupler 160 a shown in this Figure. In one arrangement, the coupler 160 a has a receptacle 168 in which is formed a bore 170 for receiving an optional booster charge 172 and an end of a detonator cord 174. The detonator cord 174 is energetically connected to the shaped charge 116. Upon receiving sufficient thermal energy from the cartridge assembly 200 b (FIG. 1), as described below, the booster charge 172 detonates, which detonates the detonator cord 174. The detonation train then detonates the shaped charge 116. It should be understood that the booster charge 172 is optional and may be omitted in embodiments wherein the detonator cord 174 can be directly detonated.

FIG. 8 illustrates the energetic connection between the cartridge assembly 200 a and the coupler 160 a. A similar energetic connection is present between the cartridge assembly 200 b and the coupler 160 b. Referring to FIGS. 8 and 6A, the switch 180 may include an initiating element 188. The initiating element 188 applies activating energy for detonating the detonator cord 174 or the booster 172 in response to an activation signal (e.g., electrical energy). In some embodiments, the initiating element 188 may be formed of a metal that is resistant to electrical flow and generates heat when electrical current is applied. The initiating element 188 may act directly on and detonate the detonator cord 174. In other embodiments, the initiating element 188 may act on the booster charge 172 disposed in the receptacle 170 and positioned immediately adjacent to the initiating element 188. When fully assembled, the booster charge 172 may be in physical contact with or spatially separated from the initiating element 188. Nevertheless, the booster charge 172 is sufficiently close enough to be detonated by the thermal energy emitted by the initiating element 188. The booster charge 172 and/or the detonator cord 174 may be formed of energetic materials include, but are not limited to, RDX (cyclotrimethylenetrinitramine or hexahydro-1,3,5-trinitro-1,3,5-triazine), HMX (cyclotetramethylenetetranitramine or 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane), TATB (triaminotrinitrobenzene), FINS (hexanitrostilbene), and other similar materials that are formulated to generate a high order output (i.e., thermal energy and shock waves). Detonation of the booster charge 172 thereafter detonates the detonator cord 174, which carries the detonation to one or more shaped charges 116 of the perforating gun 112.

To fire the perforating gun 110, the second firing signal is transmitted via the signal conducting carrier 290 to the perforating tool 100. The second firing signal is communicated to the cartridge 200 a in a manner previously described. In this instance, however, the switch 180 (FIG. 6A) recognizes that the second firing signal is an instruction to firing the perforating gun 110. Thus, instead of passing on the signal, the switch 180 (FIG. 6A) initiates the firing of the perforating gun 110 in a manner previously described.

Referring to FIGS. 1 and 7, embodiments of the present disclosure form fluid-tight seals between the bulkhead 130 a,b and an inner surface 140 defining an inner bore of the carrier 111. Referring to FIG. 7, two carriers, carriers 111 a and 111 b, are shown connected at a threaded connection 252. It should be noted that, in this embodiment, at the threaded connection 252, there are no sealing elements forming a seal between the surface of carrier 111 a and carrier 111 b. That is, there is only metal-to-metal contact between the carriers 111 a,b and there are no interposed members, such as o-rings, that forms seals between the contacting surfaces of the carriers 111 a,b. Additionally, may be metal-to-metal contact between the carriers 111 a,b and the bulkheads 130 a,b. Instead, the sealing elements 138 only form seals between the bulkhead 130 a,b and the inner surface 140. A similar sealing arrangement is present at the uphole end 280 adjacent to the end cap 292. In other embodiments one or more seals (not shown) may be at the threaded connection 252.

Additionally, embodiments of the present disclosure isolate a perforating gun interior from the shockwaves from the firing of an adjacent perforating gun. Referring to FIG. 7, the bulkhead 130 may be formed with sufficient axial thickness and of a material sufficiently strong to prevent the pressure waves and shock from one perforating gun from affecting an adjacent gun. In one arrangement, the bulkhead may have a first of seals 138 a forming a seal with a first carrier 111 a and a second set of seals 138 b forming a seal with a second carrier 111 b. The bulkhead 130 may be fixed between a first interior torque shoulder 254 a of the first carrier 111 a and a second interior torque shoulder 254 b of the second carrier 111 b. Thus, when the carriers 111 a,b are threaded together at a threaded connection 256, the bulkhead 130 is compressed between the torque shoulders 254 a,b. In some embodiments, the toque shoulder 254 a,b may be formed on other locations of the carriers 111 a,b. As noted previously, seals 139 form a fluid barrier between the contact assemblies 146 a,b and the bulkheads 130 a,b respectively.

Referring to FIG. 9, there is shown another embodiment of a perforating tool 100 in accordance with the present disclosure. The perforating tool 100 may include a first gun assembly 110 and a second gun assembly 112. Each gun assembly 110, 112 includes a carrier 111 that is shaped to receive a charge tube 114. Each gun assembly 110, 112 also includes one or more shaped charges 116 fixed within the charge tube 114. To enable selectively firing the gun assemblies 110, 112, a select fire system may be used in which a cartridge assembly 300 a is programmed to only fire the first gun assembly 110 and a cartridge assembly 300 b is programmed to only fire the second gun assembly 112. Illustrative arrangements according to the present disclosure for enabling such select firing are described below.

Referring now to FIG. 10, the gun assembly 110 in accordance with one embodiment of the present disclosure is shown in an isometric view. For clarity, the carrier 111 (FIG. 9) is not shown. In this embodiment, the charge tube 114 may be formed as a tubular member having a first end 118, a second end 120, and an interior bore 122. The charge tube 114 provides a receiving structure to which the shaped charges 116, a bulkhead 130 a, and a coupler 400 a are secured. The bulkhead 130 a may be fixed to the first end 118 with a suitable fastening element 132, such as a screw.

The charge tube 114 may include a first opening 148 through which the shaped charge 116 may be inserted into the interior bore 122 and a second opening 151 through which a detonator cord 174 may be inserted into the interior bore 122. The charge tube 114 also includes one or more slots 462 for receiving the coupler 400 a.

The coupler 400 a provides a bay into which the cartridge assembly 300 a (FIG. 9) can be inserted during assembly of the perforating tool 100 (FIG. 9). Upon insertion, the cartridge assembly 300 a (FIG. 9) becomes operatively engaged with the coupler 400 a: i.e., physically connected to the structure of the perforating tool 100 (FIG. 9), electrically coupled into the signal communication wiring of the perforating tool 100 (FIG. 9), and energetically coupled to the ballistic assembly, which include the detonator cord 174 and optional booster charge (not shown). As further described below, the use of sliding surfaces and biased connections enable the structural, electrical connections, and energetic connections to be made principally during insertion and with minimal additional handling. FIG. 11A is a sectional isometric view of the cartridge assembly 300 a positioned within the coupler 400 a. FIG. 11B is an isometric view of the coupler 400 a. FIG. 11C is an end view of the coupler 400 a.

Referring to FIGS. 11A-C, in one embodiment, the coupler 400 a may include a hollow body 402 having a tubular receptacle 404 that communicates with an interior 406 and a coupler contact 408.

Referring to FIG. 11C, the tubular receptacle 404 extends from the body 402 and includes a bore 410. The bore 410 is sized and shaped to receive an end 412 of the detonator cord 174 (FIG. 10) and optionally a booster charge 414. The coupler contact 408 includes a coupler contact surface 416 and a wiring contact 420. The coupler contact surface 416 may be formed on a body, such as, plate, a rod, tube, fastener, or other electrically conductive member that is exposed to the interior 406. The wiring contact 420 may be an eyelet, fastener, hook, frame, or other member that is exposed to an exterior of the body 402 and has at least a portion that is electrically conductive. The wiring contact 420 is electrically connected to a signal conducting carrier, such as a wire 176. Referring to FIGS. 11B and C, wings 422 formed on an external surface of the body 402 may be sized and shaped to be closely received into complementary slots 462 (FIG. 10) formed at the end 120 (FIG. 10) of the charge tube 114. The coupler 400 b is generally of the same construction as that of the coupler 400 a.

Referring to FIGS. 12A-B, there is schematically shown a cartridge assembly 300 a in accordance with one embodiment of the present disclosure that is housed at least partially within the interior 406 of the coupler 400 a (FIG. 11 B and C). Cartridge assembly 300 b may use a similar configuration as cartridge assembly 300 a. FIG. 12A is a top view of the cartridge assembly 300 a that omits an upper section so that the interior may be visible. FIG. 12B is an isometric view of the cartridge assembly 300 a.

As will be apparent from the discussion below, the cartridge assembly 300 a acts as a structural and electrical adaptor that enables switches of various different configurations and sizes to be used in the perforating tool 100 (FIG. 9). Exemplary switches 180, 181 that may be operatively connected to the cartridge assembly 300 a have already been described in connection with FIGS. 6A-B.

In one embodiment, the cartridge assembly 300 a includes a body 302 in which a cavity 304 is formed and electrical contact assemblies for communicating signals to and from the switch 180 (FIG. 6A). The body 302 is sized to be received into the interior 406 of the coupler 400 a (FIGS. 11B and C). The cavity 304 is sized and shaped to house the switch 180 (FIG. 6A). In one arrangement, the electrical assemblies include a throughput contact 308 and an input contact 310 to form electrical connections with the switch 180 (FIG. 6A).

The input contact 310 conveys a received signal to the switch 180 (FIG. 6A) inside the cartridge assembly 300 a. The input contact 310 may include a resilient external input contact 322 that projects from an exterior wall 326 of the body 302. The external input contact 322 may be sized to present a contact surface that is biased away from the body 302. The biasing allows the external input contact 322 to compressively and physically contact the coupler contact surface 416 (FIG. 11A). The input contact 310 may have an end 328 positioned within the cavity 304 and that is suitable to electrically connect with the electrical input 184 (FIG. 6A) of the switch 180 (FIG. 6). The input contact 310 may be a spring, plate, pad, or other conductive element. In one embodiment, the input contact 310 is formed as continuous thin electrically conductive plate. In other embodiments, the input contact 310 may be formed of two or more elements.

FIG. 11A illustrates the signal transmission interface and signal transfer via the input contact 310 of the cartridge assembly 300 a. A signal communication path is formed when the external input contact 322 of the cartridge assembly 300 a (FIG. 12A) electrically couples to the coupler contact surface 416 of the coupler 400 a, which is in electrical communication with the wiring contact 420. Therefore, when the electrical contact surface 322 of the cartridge 200 a (FIG. 12A) contacts the coupler contact surface 416, a signal conducting circuit is formed between the wire 176 and the switch 180 (FIG. 6A) inside the cartridge assembly 300 a (FIG. 12A).

The throughput contact 308 conveys the signal received by the cartridge assembly 300 a to another cartridge assembly, here the cartridge assembly 300 b (FIG. 9). The signal may be the same as or similar to the received signal or a new signal. The throughput contact 308 may include an external throughput contact 332 and an end 334. The external throughput contact 332 may be sized to present a contact surface that is biased away from the body 302 to compressively and physically contact the conductive tip 251 (FIG. 13) as described later. The end 334 terminates within or near the cavity 304 and may be electrically connected to the electrical output 186 (FIG. 6A) of the switch 180 (FIG. 6). In one embodiment, the throughput contact 308 is formed as continuous thin electrically conductive plate. In other embodiments, the throughput contact 308 may be formed of two or more elements.

In embodiments, the cartridge assembly 300 may also include a grounding contact 340 for electrically grounding the switch 180 (FIG. 6). The grounding contact 340 may include an end 342 positioned in the cavity 304 and an external ground contact 344. The external ground contact 344 may be in electrical contact with an inner surface of the charge tube 114 or bulkhead 130 b (FIG. 2). The end 342 terminates within or near the cavity 304 and may be electrically connected to the ground wire 194 (FIG. 6A) of the switch 180 (FIG. 6). In one embodiment, the grounding member 340 is formed as continuous thin electrically conductive plate. In other embodiments, the grounding member 340 may be formed of two or more elements.

The cartridge assembly 300 a further includes a cradle 350 for receiving the initiating element 188 (FIG. 6A)). Referring to FIGS. 11 A and 12A, the cradle 350 is sized and shaped to position the initiating element 188 (FIG. 11A) sufficiently close to detonate the detonating cord end 412 and/or booster 414 in the tubular receptacle 404 in a manner already previously described; i.e., form an energetic connection. The cradle 350 may communicate with the cavity 304 using suitable openings (not shown) that can accommodate hardware and wiring.

Referring to FIG. 11A, 12A and FIG. 6A, it should be noted that the cradle 350 and the cavity 304 are oriented to position the switch 180 and the initiating element 188 in a parallel, or side-by-side, relative alignment. That is, the switch 180 and the initiation element 188 at least partially overlap along a longitudinal axis of the perforating tool 100 (FIG. 9), the longitudinal axis being an axis that passes through centers of the ends 118, 120 of the charge tube 114 (FIG. 9). In some embodiments, the switch 180 and the initiation element 188 may have different radial offsets or distances from the longitudinal axis. In further embodiments, an annular space relative to the longitudinal axis may separate the switch 180 and the initiation element 188. Consequently, when inserted into the perforating tool 100 (FIG. 9), the switch 180 and the initiation element 188 also at least partially overlap along a longitudinal axis of the perforating tool 100 (FIG. 9). As should be appreciated, the parallel, side-by-side arrangement occupies less total axial distance along the longitudinal axis than a serial, end-to-end arrangement. Additionally, in certain embodiments, the longitudinal axis may intersect the initiation element 188. That is, the initiation element 188 may centrally positioned at or concentric with the longitudinal axis and the switch 180 may be radially offset from the initiation element 188 and the longitudinal axis. Also, as best seen in FIG. 12B, a lid 360 may be used to enclose the switch 180 (FIG. 6) within the cavity 304.

FIG. 13 illustrates the signal transmission interface and signal transfer via the throughput contact 308 of the cartridge assembly 300 a. A signal communication path is formed when the external throughput contact 332 of the cartridge assembly 300 a electrically couples to the contact assembly 146 b in the bulkhead 130 b. As described previously, the contact assembly 146 b includes a signal conducting tip 251 on one end and a connection with a wire 176 b at the other end. The wire 176 b is in signal communication with the cartridge assembly 300 b (FIG. 9). Therefore, when the tip 251 contacts the external throughput contact 332 of the cartridge assembly 300 a, a signal conducting circuit is formed across the bulkhead 130 b such that the first firing signal can be communicated from the cartridge assembly 300 a of the perforating gun 110 to the cartridge assembly 300 b of the perforating gun 112 (FIG. 9).

Like embodiments previously described, it should be appreciated that the switch 180 (FIG. 6A) may be pre-installed in the cartridge assembly 300 a prior to assembly of the perforating tool 100 (FIG. 9). This pre-installation may include making electrical connections between the electrical input 184, electrical output 186, and ground 194 (FIG. 6A) of the switch 180 (FIG. 6A) and the ends 328, 334, 342, respectively, (FIG. 12A). The electrical connections may be made by known techniques such as soldering, splicing, etc. Later installation simply requires sliding the cartridge assemblies 300 a,b (FIG. 9) inside the couplers 400 a,b (FIG. 10), respectively, of the perforating tool 100 (FIG. 9) to form the electrical connections.

Referring to FIG. 9, the gun assembly 112 also includes features similar to those described in connection with the gun assembly 110, e.g., a cartridge assembly 300 b, a bulkhead 130 b, a coupler 400 b, etc. and uses the same construction as gun assembly 110, although in other embodiments a different construction may be used.

Referring to FIGS. 9 and 10, in one illustrative mode of assembly, two or more perforating guns, e.g., guns 110, 112, may be assembled with wiring 176 a,b and the components required to form a ballistic train (e.g., detonating cord 174, shaped charges 116, etc) but without the cartridge assembly 300 a, which contains the addressable switch 180 and initiating element 188 (FIG. 6A). The wiring 176 winds around an outer surface 361 of the charge tube 114 and connects to the external contact member 408 (FIG. 11A) which is positioned on wing 422 a. While not visible in FIG. 10, it should be appreciated that the external contact member 408 is positioned external to the charge tube 114 such that an electrical connection with the wiring 176 can be readily made.

Thereafter, the perforating guns 110, 112 may be shipped to a rig site. At the rig site, the cartridge assembly 300 a is inserted into the coupler 400 a and the cartridge assembly 300 b engages the coupler 400 b upon being inserted into the coupler 400 b. It should be noted that the engagement is accomplished without removing or disassembling the charge tube assembly. A similar procedure is used if three or more perforating guns are present. Thereafter, the gun assemblies may be connected sequentially.

It should be noted that the assembly at the rig site forms electrical and energetic connections at the same time that perforating gun 100 is assembled. For example, sliding the cartridge assembly 300 a into the coupler 400 a physically and electrically couples the coupler contact surface 416 with the external input contact 322. The external input contact 322 may be a spring-like biased body that can compress into a biased engagement with the coupler contact surface 416. Sliding the cartridge assembly 300 a into the coupler 400 a also physically positions the initiating assembly 188 (FIG. 11A) close enough to the detonator cord end 412 (FIG. 11A) or booster 414 (FIG. 11A) to form an energetic connection therebetween. Also, installing the bulkhead 130 b onto the end 118 of the charge tube 114 physically and electrically couples the resilient external throughput contact 332 and the conductive tip 251 as well as the contact 340 and a surface of the charge tube 114 or the bulkhead 130 b. The external throughput contact 332 may also be a spring-like biased body that can compresses into a biased engagement with the conductive tip 251. Likewise, the contact 340 may be a spring-like biased body that can compresses into a biased engagement with the bulkhead 130 b or charge tube 114.

The operation of the FIGS. 9-13 embodiments is generally similar to the perforating guns and assemblies previously described. Referring to FIG. 9, in one exemplary mode of operation, the perforating gun closest to the downhole end 282, here perforating gun 112, is fired first. Thereafter, the next most adjacent perforating gun uphole of the fired perforating gun, here perforating gun 110, is fired. To facilitate sequential “bottom up” firing of the perforating tool 100, multiple firing signals may be sent. For instance, a first firing signal may be sent to fire the perforating gun 112 and a second firing signal may be sent to fire the perforating gun 110. As further described below, the cartridge assembly 300 a is programmed to pass the first firing signal to the cartridge 300 b. The cartridge 300 b is programmed to fire the perforating gun 112 upon receiving the first firing signal. The cartridge 300 a is programmed to fire the perforating gun 110 upon receiving the second firing signal. If more than two gun assemblies are present, then three or more cartridge assemblies, couplers, and associated firing signals may be needed. However, as described in with FIG. 14 later, the signal direction can be reversed by transmitting the firing signal to throughput contacts 308 and passing firing signals through the input contacts 310. That is, the cartridges 300 a,b are bi-directional.

To initiate firing, the first firing signal may be transmitted from a surface location to the perforating gun 100 by a signal conducting carrier 290. A signal receiving interface for receiving the first firing signal is provided in the end cap 292. The signal transfer assembly 146 a includes a signal conducting tip 251 on one end and a connection with a wire 176 a at the other end. The wire 176 a is in signal communication with the cartridge assembly 300 a via the coupler contact 408 (FIG. 11A). Therefore, when the tip 251 electrically engages the signal conducting carrier 290, a signal conducting circuit is formed across the bulkhead 130 a such that the first firing signal can be communicated from the signal conducting carrier 290 via wire 176 a to the coupler contact 408 and then to the switch 180 (FIG. 6A) inside the cartridge assembly 300 a (FIG. 12A).

Referring to FIG. 11A, the first firing signal travels from the coupler contact 408 to the electrical input 184 (FIG. 6A) of the switch 180 (FIG. 6A). Because the switch 180 (FIG. 6A) is programmed to fire the gun assembly 110 (FIG. 1) only after receiving the second firing signal, the switch 180 (FIG. 6A) passes the first firing signal to the throughput contact 308 (FIG. 12a ). Referring to FIG. 13, the first firing signal travels via the external throughput contact 332 of the throughput contact 308 and the signal conducting tip 251 to the wire 176 b. Thereafter, the first firing signal travels via the wire 176 b to the cartridge assembly 300 b. Because switch 180 (FIG. 6A) in cartridge assembly 300 b is programmed to recognize that the first firing signal is for firing the perforating gun 112, the switch 180 (FIG. 6A) initiates the firing of the perforating gun 112.

To fire the perforating gun 110, the second firing signal is transmitted via the signal conducting carrier 290 to the perforating tool 100. The second firing signal is communicated to the cartridge 300 a in a manner previously described. In this instance, however, the switch 180 (FIG. 6A) recognizes that the second firing signal is an instruction to firing the perforating gun 110. Thus, instead of passing on the signal, the switch 180 (FIG. 6A) initiates the firing of the perforating gun 110 in a manner previously described.

Referring to FIG. 14, there is shown another embodiment of a perforating tool 100 in accordance with the present disclosure. The perforating tool 100 may include a first gun assembly 110 and a second gun assembly 112, which include features previously discussed such as associated bulkheads 130 a,b, respectively. To initiate firing, the first firing signal may be transmitted from a surface location to the perforating gun 100 by a signal conducting carrier 290. To enable selectively firing the gun assemblies 110, 112, a select fire system may be used in which a cartridge assembly 300 a is programmed to only fire the first gun assembly 110 and a cartridge assembly 300 b is programmed to only fire the second gun assembly 112. The cartridge assembly 300 a has an associated coupler 400 a. The cartridge assembly 300 b has an associated coupler 400 b.

In the FIG. 14 arrangements, the firing signals are conveyed in an opposite direction through the cartridge assemblies 300 a,b as compared to the FIG. 9 arrangement. That is, the firing signals are conveyed by the signal conducting carrier 290 to the throughput contact 308 a. Depending on the firing signal, the firing signal either fires the gun assembly 110 or passes the firing signal via the input contact 310 a to the gun assembly 112. Thus, the throughput contact 308 a can receive a signal to fire switch 180 inside cartridge 300A or can pass the firing signal to input contact 310 a to the switch 180 (FIG. 6A) inside the cartridge assembly 300 b.

As used in this disclosure, the terms “aligned” means co-linear or concentric. Thus, axes that are aligned are concentric. Axes that are misaligned or eccentric are separated by a predetermined distance. As used in this disclosure, terms such as “substantially,” “about,” and “approximately” refer to the standard engineering tolerances that one skilled in the art of well tools would readily understand.

As used herein, an “electrical connection” or “electrical engagement” is a connection wherein electrical signals are conveyed between two or more objects. Physical contact between the two bodies may or may not be present.

It is also reiterated that devices according to the present disclosure may be used in conjunction with the switch 180, the switch 181 or any other switch configuration, whether or not addressable.

The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope of the invention. It is intended that the following claims be interpreted to embrace all such modifications and changes. 

1. An apparatus for use in a wellbore, comprising: a first gun assembly having: a first charge tube having a longitudinal axis defined by an axis that passes through centers of opposing ends of the charge tube; a first detonator cord disposed along the first charge tube, a first signal-conveying wire disposed along the first charge tube, a first coupler affixed to an end of the first charge tube, the first coupler including: a receptacle receiving an end of the detonator cord, and a coupler contact electrically connected to the first signal conveying wire, and a first cartridge assembly including: a body, an input contact positioned on the body and electrically coupled to the coupler contact, a throughput contact positioned on the body, a switch disposed in the body, the switch being electrically connected to the input contact and the throughput contact, and an initiating element disposed in the body and electrically connected to the switch, the initiating element being energetically coupled to the end of the detonator cord in the receptacle, wherein the switch and the initiating element at least partially overlap along the longitudinal axis; and a first signal transfer assembly electrically coupled to the throughput contact; and a second gun assembly having: a second charge tube, a second detonator cord disposed along the second charge tube, a second signal-conveying wire disposed along the second charge tube, the second signal-conveying wire being electrically coupled to the first contact assembly, a second coupler affixed to an end of the second charge tube, the second coupler including: a receptacle receiving an end of the second detonator cord, and a coupler contact electrically connected to the second signal conveying wire; and a second cartridge assembly including: a body, an input contact electrically positioned on the body and coupled to the second coupler contact, a throughput contact positioned on the body, a switch disposed in the body, the switch being electrically connected to at least the input contact, and an initiating element disposed in the body and electrically connected to the switch, the initiating element being energetically coupled to the end of the second detonator cord in the receptacle.
 2. The apparatus of claim 1, wherein the switch of the second cartridge is also connected to the throughput contact of the second cartridge, and wherein the second gun includes a second signal transfer assembly electrically coupled to the throughput contact of the second cartridge assembly, and further comprising: a third gun assembly having: a third charge tube, a third detonator cord disposed along the third charge tube, a third signal-conveying wire disposed along the third charge tube, the third signal-conveying wire being electrically coupled to the second contact assembly, a third coupler affixed to an end of the third charge tube, the third coupler including: a receptacle receiving an end of the third detonator cord, and a coupler contact electrically connected to the third signal conveying wire; and a third cartridge assembly including: a body, an input contact electrically positioned on the body and coupled to the third coupler contact, a throughput contact positioned on the body, a switch disposed in the body, the switch being electrically connected to at least the input contact, and an initiating element disposed in the body and electrically connected to the switch, the initiating element being energetically coupled to the end of the third detonator cord in the receptacle.
 3. An apparatus for use with a gun assembly having charge tube with a longitudinal axis defined by an axis that passes through centers of opposing ends of the charge tube, a detonator cord disposed along the charge tube, and a signal-conveying wire disposed along the charge tube, the apparatus comprising: a switch having an initiating element; a coupler configured to be received at an end of the charge tube, the coupler including: a receptacle receiving an end of the detonator cord, and a coupler contact electrically connected to the signal conveying wire; and a cartridge assembly engagable with the coupler, the cartridge assembly including: a body configured to receive the switch and the initiating element, an input contact positioned on the body, and a throughput contact positioned on the body,  wherein engaging the cartridge assembly with the coupler simultaneously electrically couples the input contact to the coupler contact and energetically couples the initiating element with the end of the detonator cord, and  wherein the switch and the initiating element are positioned in a parallel, side-by-side arrangement to at least partially overlap along the longitudinal axis.
 4. The apparatus of claim 3, wherein the initiation element is intersected by the longitudinal axis and the switch is radially offset from the longitudinal axis.
 5. The apparatus of claim 3, wherein the switch and the initiating element partially overlap along the longitudinal axis.
 6. The apparatus of claim 3, wherein the initiating element is a metal member configured to generate heat with the application of electrical energy.
 7. The apparatus of claim 3, wherein the initiating element is configured to output sufficient thermal energy to detonate an energetic material.
 8. The apparatus of claim 7, wherein the energetic material is one of: (i) the detonator cord, and (ii) a booster charge.
 9. The apparatus of claim 3, wherein the switch is programmed to initiate the firing of a selected perforating gun of a plurality of perforating guns.
 10. The apparatus of claim 3, wherein the coupler includes a body having an interior in which the cartridge assembly is received.
 11. The apparatus of claim 10 wherein the coupler contact includes a coupler contact surface and a wiring contact, wherein the coupler contact surface is an electrically conductive member that is exposed to the interior of the body, and wherein the wiring contact has a electrically conductive portion that is exposed to the exterior of the body.
 12. The apparatus of claim 11, wherein the input contact includes an external input contact that projects from an exterior wall of the body, the external input contact configured to compressively contact the coupler contact surface.
 13. The apparatus of claim 12, wherein the input contact further includes an end configured to electrically connect with the switch.
 14. The apparatus of claim 13, wherein the throughput contact includes an external throughput contact and an end, wherein the external throughput contact is configured to electrically connect with the switch, and wherein the end is configured to electrically connect with an adjacent cartridge assembly.
 15. A method for perforating a formation, comprising: forming a perforating tool with a plurality of gun assemblies; configuring a selected gun assembly of the plurality of gun assemblies to have: a charge tube having a longitudinal axis defined by an axis that passes through centers of opposing ends of the charge tube; a detonator cord disposed along the charge tube, a signal-conveying wire disposed along the charge tube, a switch having an initiating element; a coupler configured to be received at an end of the charge tube, the coupler including: a receptacle receiving an end of the detonator cord, and a coupler contact electrically connected to the signal conveying wire; and a cartridge assembly engagable with the coupler, the cartridge assembly including: a body, an input contact positioned on the body, and a throughput contact positioned on the body,  wherein engaging the cartridge assembly with the coupler simultaneously electrically couples the input contact to the coupler contact and energetically couples the initiating element with the end of the detonator cord, and  wherein the switch and the initiating element are positioned in a parallel, side-by-side arrangement to at least partially overlap along the longitudinal axis; conveying the perforating tool into a wellbore formed in the formation; and transmitting a firing signal to fire the selected gun assembly.
 16. The method of claim 15, further comprising programming the switch to initiate the firing of the selected perforating gun of a plurality of perforating guns.
 17. The method of claim 15, wherein the coupler includes a coupler body having an interior in which the cartridge assembly is received.
 18. The method of claim 17, wherein the coupler contact includes a coupler contact surface and a wiring contact, wherein the coupler contact surface is an electrically conductive member that is exposed to the interior of the coupler body, and wherein the wiring contact has a electrically conductive portion that is exposed to the exterior of the coupler body.
 19. The method of claim 17, wherein the input contact includes an external input contact that projects from an exterior wall of the coupler body, the external input contact configured to compressively contact the coupler contact surface.
 20. The method of claim 15, further comprising: configuring a second selected gun assembly of the plurality of gun assemblies to have: a charge tube having a longitudinal axis defined by an axis that passes through centers of opposing ends of the charge tube; a detonator cord disposed along the charge tube, a signal-conveying wire disposed along the charge tube, a switch having an initiating element; a coupler configured to be received at an end of the charge tube, the coupler including: a receptacle receiving an end of the detonator cord, and a coupler contact electrically connected to the signal conveying wire; and a cartridge assembly engagable with the coupler, the cartridge assembly including: a body, an input contact positioned on the body, and a throughput contact positioned on the body,  wherein engaging the cartridge assembly with the coupler simultaneously electrically couples the input contact to the coupler contact and energetically couples the initiating element with the end of the detonator cord, and  wherein the switch and the initiating element are positioned in a parallel, side-by-side arrangement to at least partially overlap along the longitudinal axis; and transmitting a second firing signal to fire the second selected gun assembly. 